Tungsten is an important commercial material for the production of e.g., cemented carbides, which are useful for shaping metals, wood, composites, plastics, and ceramics and which are useful in the mining and construction industries. Tungsten is also useful as an element of an alloying material that can be used in steel production. Additionally, tungsten is employed in such applications as lighting filaments, electrodes, electrical and electronic contacts, wires, and metal sheets. For such industrial uses, the principal commercial intermediate that is desired is ammonium paratungstate; accordingly, tungsten is commonly obtained and converted to such a form for various applications.
Likewise, vanadium is also an important commercial material, known to be used in producing rust-resistant springs and high-speed tool steels. Vanadium pentoxide (V2O5) is known to be used in ceramics, as a catalyst, and in the production of superconductive magnets, and vanadyl sulfate and sodium metavanadate have been used as dietary supplements.
Numerous natural sources of tungsten exist; however, in such sources, tungsten is generally found in combination with one or more other metals. For example, tungsten is commonly found in ores in the form of wolframite (a tungstate of iron and manganese) and scheelite (native calcium tungstate). Numerous secondary sources of tungsten are also known, e.g., from recycling of used tungsten-based materials such as spent catalysts, metal tools, filaments, and the like. Isolation of tungsten from these and other sources and, specifically, separation of tungsten from other metals is often a limiting factor of the use of such sources to obtain tungsten.
For example, significant attention has been focused on separating tungsten from molybdenum. See, for example, U.S. Pat. No. 3,158,438 to Kurtak; U.S. Pat. No. 3,607,008 to Chiola et al.; U.S. Pat. No. 3,969,478 to Zelikman et al.; U.S. Pat. No. 4,275,039 to Ozensoy et al.; U.S. Pat. No. 4,328,190 to Beckstead et al, which are incorporated herein by reference. Another impurity that can hamper the isolation of tungsten from various sources is vanadium; however, few methods are reported for the separation of tungsten and vanadium. The few methods that are known involve precipitation methods for the selective removal of tungsten from mixtures comprising tungsten and vanadium. See Luo et al., Minerals Engineering 16:665-670 (2003); Luo et al., Hydrometallurgy 72(1-2): 1-8 (2004); and U.S. Patent Application Publication No. 2013/0283975 to Kiyosawa et al., which are incorporated herein by reference in their entireties. One method for separating tungsten and vanadium involves electroreduction of vanadium (V) in solution to vanadium (IV) and subsequent sorption of tungsten in the solution onto a selective resin to retain the tungsten and elute the vanadium. See Durisova, Sep. Sci. Tech. 44, 12:2750-2760 (1999), which is incorporated herein by reference. Known methods generally offer low selectivity, require a long reaction time, and/or are applicable only for materials with low metal concentrations, rendering them of limited applicability for many applications.
It would be beneficial to provide effective methods for the isolation of tungsten from mixtures comprising vanadium (i.e., separation of tungsten and vanadium), particularly methods that are applicable across a wide range of metal concentrations. Environmental and sustainability benefits of such methods extend not only to the recovery of tungsten and vanadium, which can be recycled into usable products, but also to decreasing the amount of tungsten and vanadium which must be extracted for ores and recycling catalysts for nitrogen oxide/NOx reduction (deNOx catalysts), which otherwise would be disposed of in a landfill.